1. Field of the Invention
This invention relates to a catheter or probe with a sensor for placement within a human or animal to allow direct monitoring within the body, and more particularly, relates to a flexible multiconductor and the support of a fine pitch thereof which connects the in vivo sensor to the ex vivo monitor by passing through a catheter lumen. A method of making such a multiconductor also relates to this invention.
2. Background
Catheters have been inserted into humans and animals for diagnosis, monitoring and treatment purposes and such catheters have to be small and flexible in size and structure in order to function without irritating the body part into which they are placed. Conductors used to transmit signals from the distal end to the proximal end of a catheter are in cross section smaller than the catheter lumen in order to be fed through the lumen. As circuit features on semiconductor devices and on active and passive monolithic electronic components continue to shrink and denser integrated circuit configurations are commercialized, microelectronic interconnect technology is being challenged to down-size fine pitch leads to keep pace with the smaller input/output port geometries on these chips. The densely packed porting pads of microchips enable electrical intercommuniation, via miniature mechanical links, between adjacent microelectronic devices, their support substrate and peripheral on-board microcircuit elements. As a result, interconnect lead pitches are approaching 0.10 mm on 0.05 mm wide terminals with 0.05 mm spaces.
If a sample of body fluid is removed from a patient by a catheter for purposes of analysis, the sample has to be taken to a laboratory, analysis made and the results transmitted to the doctor. Delay in performing the analysis and transmitting the data could be fatal to the patient. Significant advances have been achieved in providing continuous patient monitoring but most systems rely on ex vivo sensors. A use of a catheter and administration line is to provide a hydraulic column for transmitting pressure readings to an external sensor. Although there are many kinds of sensors capable of monitoring bodily functions, a commonly used sensor is for reading pressure. In connection with externally placed pressure sensors, the hydraulic column needed to transmit the signal has problems of air bubbles, kinks in the tubing about the column and blood clots, any of which could affect the reliability, the waveform fidelity and the accuracy and the precision of the signals.
An in vivo probe with a tip mounted sensor solves such problems and presents additional difficulties due to the reduced size of the sensor necessitated by the space available in the introducer used to penetrate small vessels in the body. The probe catheter should be about twenty gauge to provide an instrument for therapy or diagnosis which is easily inserted and easy to use without irritation or injury to the patient's vasculature. Twenty gauge catheters are commonly used on all but pediatric patients without problems of insertion or irritation when using such catheters, particularly, in connection with peripheral vessels. A pressure sensor on the distal tip of a twenty gauge catheter or probe would eliminate the need for a hydraulic column and the attendant difficulties.
Catheter tip pressure sensors have been relatively large in size, complicated in design, and costly to manufacture and use; therefore, such catheters have not been disposable. For preventing spread of disease and infection, an inexpensive and reliable single use catheter tip pressure sensor is desired. A design for a small, simple to manufacture catheter tip pressure sensor coupled with a design and method for making a multiconductor and support small enough to fit within the bore of a 20 gauge catheter would facilitate the development of a single-use catheter assembly for intra vascular blood pressure measurement.
Catheters with sensors at the distal tip thereof include U.S. Pat. No. 3,710,781 wherein a pair of elongate pressure sensor elements mounted on opposite sides of a support permit as large a sensor area as practical for purposes of providing accurate reproductions of blood pressure wave forms. U.S. Pat. No. 3,480,083 has an apparatus for measuring esophageal squeezing pressure; pressure sensitive sensors spaced lengthwise along and resiliently mounted on the catheter tube measure variations in pressure while the catheter is in or passing through the esophagus. The sensors are miniaturized discrete electronic components connected to a pressure responsive diaphragm and are supported within the tube by cylindrical holders fit therein to carry the exterior surface of the diaphragm. U.S. Pat. No. 4,772,761 has a sealed electrical circuit made on a metal stamping attached to a housing molded of a dielectric. The housing carries electronic components.
U.S. Pat. No. 3,545,275 has a device responsive to impedance used for measuring pressure with a miniaturized sensor. The sensor is responsive to diaphragm fluctuations where the diaphragm is mounted in the distal end of a small diameter tube. A small probe is disclosed in U.S. Pat. No. 3,811,427 wherein a pair of electrodes are mounted in a liquid filled chamber and are sensitive to fluctuations in a diaphragm mounted at the distal end of a catheter tube. The probe is said to be smaller than one millimeter. U.S. Pat. No. 4,874,499 has a microchip sensor capable of measuring a variety of chemicals at once. The sensor has materials that develop electrical charges in the presence of the specific chemical, like potassium or calcium.
U.S. Pat. No. 4,274,423 shows a catheter tip pressure transducer electrically connected by a series of parallel wires, no structure for the wire or cable is disclosed. U.S. Pat. No. 4,610,256 appears to have a cable composed of a plurality of wires in a channel which runs through a molded plug and communicates with the atmospheric pressure. U.S. Pat. No. 4,722,348 discloses conductors which extend through the lumen of a catheter to a power supply and detector circuit. The transducer is held to the catheter by a tape and an opening is provided to expose the bonding pads on the semi-conductor so that electrical connections can be made with the conductors on the pad and the conductors passing through the lumen of the catheter.
U.S. Pat. No. 3,748,623 teaches a first conductor soldered to one side of a pad and a second conductor connected to an end pad. A third conductor is attached to a common junction with wire to the upper and lower faces of the end pad. While a pressure transducer on the end of a catheter with wiring running therethrough is disclosed, the use of a multiconductor and support is not. Similarly, U.S. Pat. No. 4,672,974 has electrical leads run through the catheter to external electronics. A cable sheath is provided for protection of the leads and an air vent can be included for a reference. U.S. Pat. No. 4,785,822 shows a reinforced cable using a stylet to give the cable desired rigidity for insertion. The wires in the cable are not supported in any particular fashion.
U.S. Pat. No. 3,946,724 shows connecting wires which run along a groove and attach to electrical conductors. The wires are only mounted in the support for the transducer. U.S. Pat. No. 3,939,823 shows electrical connections passing through the catheter lumen and a hollow tube to provide an air path to supply atmospheric reference pressure. U.S. Pat. No. 3,831,588 shows insulated wires connected to terminals of the sensor and the terminals of a plug while hermetically sealed to the exterior of a tube, pairs of wires are grouped together on a conduit such that there are two independent supports for each pair. U.S. Pat. No. 3,710,781 discloses wire passages communicating with the tubular shank of a support for the sensor. No support for the wires is shown in the lumen of the catheter.
U.S. Pat. No. 3,624,714 discloses wires held in place by epoxy which fills the entire cavity of the bore and an insulator bracket is inserted into a bore with a larger diameter and held in place by an interior shoulder at the junction of the larger and smaller bore diameters. The proximal end of the cable has insulated wires stripped back from the ends to expose the metal conductors for solder connections to the strain gauge and an L-bracket holds them spaced from one another for easy connection to the strain gauge leads. U.S. Pat. Nos. 2,976,865 and 2,634,721 show a plurality of conductors imbedded in the wall of a catheter.
U.S. Pat. No. 4,823,805 has a catheter tube with passages for a strain relief and for a pair of insulated wires; no self supporting cable is disclosed. A multiconductor lead having four conductors for carrying the signals from a solid state pressure transducer to a modular connector is described in U.S. Pat. No. 4,825,876. The multiconductor is stripped so the stranded wires can be tinned and soldered. That multiconductor is ex vivo as the sensor is of the external type. Consequently, the size of the multiconductor is not a significant element of that design.
Flexible printed circuits, disclosed in U.S. Pat. No. 3,936,575, suitable as a compact three dimensional chip include a metal clad laminate used to carry integrated circuits and capacitors and a fibrous based material with, for example, glass fabric which provides stiffness, chemical and heat resistance and dimensional stability to the resin film to which a metal foil is clad. The resin composition used to form the flexible, chemical and heat resistance base sheet is specifically disclosed in the '575 patent. A sheet or multiple sheets of resin is laminated to a copper, aluminum, tin, nickel or copper foil with an adhesive layer therebetween. The preferred foil thickness is about 0.05 to about 0.08 millimeters and the resin sheet is approximately 0.03 to 0.5 millileters thick.
U.S. Pat. No. 4,191,800 has a process for making electronic devices with a flexible double sided substrate having impregnated cloth or matting material with a resin composition and copper sheet attached to both sides. Of primary concern is the particular resin composition and not necessarily the size and flexibility of the device.
U.S. Pat. No. 4,353,954 has a dielectric resin coated in the wet state on the surface of a metal foil and dried to form an adhered coating without an adhesive between foil and the coating thus simplifying the manufacture by eliminating the adhesive and the pressing required to make the combination. U.S. Pat. No. 4,647,508 uses an adhesive between the flexible substrate and the conductor. The adhesive is loaded with glass to improve dimensional stability and lower the dielectric. A microglass reinforces a fluoropolymer in the adhesive between a fluoropolymer coated polyimide laminate and a copper conductive pattern.
U.S. Pat. No. 4,851,613 provides a flexible circuit board, to which components may be surface mounted, having substrates or layers of conductive materials and insulating layers. The substrates are reinforced with a woven fabric and the insulating layers have a plurality of rectangular insulating elements, each with their longer dimension transverse to the length of the substrate and spaced apart to define fold lines.
Not one of the flexible circuit configurations mentioned has a construction which would provide an extremely fine multiconductor and support useful for directly transmitting a signal from the distal to the proximal end of a long in vivo catheter. An extremely strong, but longitudinally elongate miniature multiconductor and support has not been disclosed. Consequently, assembly of a sensor in a catheter has been expensive, slow and labor intensive because of difficulties when threading wires that are separate through a lumen of the catheter for connecting the appropriate sensor pads to ex vivo circuitry.